1. Field of the Invention
The invention relates to a zinc-bromine battery with circulating electrolytes, motor-driven pumps with pump chambers, containers with a pressure equalization for the electrolytes, bipolar electrodes and separators disposed between them, which are constructed of plastic, wherein the frames of the separators and the frames of the electrodes having a greater thickness than the center part of the electrodes are welded together and electrolyte supply and return lines associated with the electrode chambers formed in this way and, if required, heat exchangers for the electrolytes.
2. Description of Background and Relevant Invention
The electro-chemical pairing of zinc and bromine is of increasing importance for the accumulation of current. These systems are used stationary for the accumulation of current in place of emergency power-generating units, such as Diesel engines and generators, for example, but also as an energy source for traction. In both cases weight is not of preponderant importance, but additional units can be employed as with the zinc-bromine battery.
However, zinc-bromine batteries are also known wherein not only the zinc is stored at the electrode, but in this case the precipitated bromine is present in a porous mass of activated charcoal. The storage capacity of such batteries is extraordinarily small and dentrites in the course of the precipitation of zinc are particularly disturbing, so that only low current densities can be employed.
Zinc-bromine batteries with two circulating electrolyte fluids have two particular advantages. On the one hand, interference because of the growth of dentrites is kept low and on the other hand it is possible to participate in the determination of the capacity of the battery by means of the amounts of circulating electrolytes.
The material for producing a zinc-bromine battery was changed more and more to the use of plastics, in particular polyolefins and in this case polypropylene. These plastics have excellent chemical resistance but, on the other hand, have various disadvantages. It is necessary to design the electrodes as well as the separators as particularly thin-walled elements, on the one hand for reasons of electrical resistance, on the other hand to minimize the use of material. However, with such thin-walled elements there is the disadvantage that the desired geometrical shape, a plane as a rule, leads to undesirable preferred flow forms even from small causes, for example different temperatures in the electrolyte or pressure differences between the anolyte and the catholyte. In this case it is necessary to take into consideration that the electrolytes flow through chambers having, for example, an area of 30 cm .times.30 cm, and the layer thickness of the flow can be from 1 mm to 2 mm. If deformations in the plastic occur, the mentioned irregularities in the flow appear, because of which different precipitations and dissolution of the zinc film occur, wherein it is possible for local heating to appear which, in turn, can result in the premature destruction of the battery.
In connection with zinc-bromine batteries made from plastics it is furthermore known that leaky spots occur again and again, for example at the edges of the electrodes and separators, even under strong mechanical pressure at the places to be sealed, so that such batteries cannot always be used.
A galvanic element, in particular a rechargeable zinc-bromine battery, is known from EP 438 044, wherein the connecting line for pressure equalization terminates in the area of the highest point of the collecting line when the element is in the normal position. It is disadvantageous in this case that the electrolyte can run out if the element is tilted, for example by 90.degree.. Possible contamination of the environment by the electrolyte would have incalculable consequences.